IN VIVO MICROPUNCTURE STUDIES: 1) Determination of mechanism and factors regulating hydrogen ion secretion in the papillary collecting duct; 2) the effect of PTH on bicarbonate transport in the proximal convoluted tubule; and 3) quantitative assessment of the role of bicarbonate "backleak" in determining net volume reabsorption across in vivo microperfused proximal tubules under various physiological conditions. IN VITRO MICROPERFUSION STUDIES: 1) Determine whether mineralocorticoids affect salt transport out of the medullary thick ascending limb of Henle; 2) examine the in vitro factors which regulate bicarbonate transport in collection duct segments with special emphasis on PCO2, amiloride, ambient HCO3, cAMP and PGE2; 3) quantitate and characterize K transport in collecting duct which is independent and dependent on mineralocorticoids; 4) characterize the nature of uric acid transport across various segments of the proximal tubule; and 5) extend studies to determine factors regulating bicarbonate transport across proximal convoluted tubule.